Changes in cyclic 3':5' nucleotide (cNMP) metabolism occur in sympathetic dysfunction. Differentiation of PC12 cells into a sympathetic neuronal phenotype is accompanied by changes distinct cNMP phosphodiesterases (PDEs). Nerve growth factor (NGF) or vanadate reduce cGMP- stimulated PDE (the PDE 2 gene product) in PC12 cells by 50 % after 24 hours. NGF does not decrease PDE 2 mRNA, but increase calmodulin- stimulated PDE (the PDE 1 gene) mRNA. Sympathetic differentiation may shift cNMP metabolism from a cGMP- regulated to a calcium-regulated state. To study this 1), PDE cDNAs from PC12 cells and sympathetic ganglia will be characterized by molecular cloning and expression. 2) NGF effects on PDE mRNA and protein expression will be assessed. 3) The role of phosphorylation in the regulation of PDE activity will be determined by phosphopeptide mapping and site directed mutagenesis and expression studies.